The top U.S. military commander, Admiral Mike Mullen, has said that wresting control of the area around the southern Afghan city of Kandahar is a "cornerstone in reversing the momentum" of the Taliban.

The chairman of the U.S. Joint Chiefs of Staff told a news conference in Kabul that seizing control of Kandahar would help to put the Afghan government in a position of strength to pursue reconciliation talks with insurgents.

"If we've learned nothing else in this long and bloody fight, it is that failure makes itself plainly obvious. Success takes longer to see. We will see success in central Helmand, but we must be patient," Mullen said.

"We must also look ahead to Kandahar. We know that as important as central Helmand has been, Kandahar is all the more so -- the very heart of the Taliban in this country."

NATO has announced plans to begin operations against the Taliban stronghold of Kandahar this summer.

Earlier this year, NATO and Afghan forces launched a major offensive against the militants in Helmand Province, which neighbors Kandahar.

On March 30, Mullen met local leaders from Marjah, the focus of the offensive, who complained to him about a lack of security and a failure to deliver on promises of civil services.